When soldering an electronic component to a predetermined face of a circuit board, a reflow furnace, a jet soldering device and the like have been used in the past. For example, in a case of soldering it in the reflow furnace, a solder paste has been used. The solder paste is produced by mixing flux and solder powder into paste. The solder paste is applied to a soldered portion of a circuit board by printing or by using a dispenser. An electronic component is mounted thereon, and then, the solder paste is heated and melted in the reflow furnace to electrically connect the circuit board and the electronic component. Generally, soldering is performed in an atmosphere filled with inert gas or in the atmosphere (air).
The flux removes an oxide film on the surface of metal to be soldered, and prevents reoxidation of the metal surface during heating in the soldering step. The flux reduces surface tension of the solder powders to improve wettability thereof. The flux has a solid component, such as pine resin, a thixotropic agent, and an activator, which is dissolved with a solvent.
In a preheating zone, especially the solvent in the flux component of the solder paste applied to the circuit board volatilizes (vaporizes) to become flux fumes, and in a main heating zone, when subjected to high temperatures, a solid component such as rosin in the flux component melted in the preheating zone also vaporizes to become fumes and floats in the furnace. When the solvent or solid component-derived fumes contact relatively cool sites in the furnace, for example, a conveyor for transferring the circuit board into the furnace, a fan for circulating hot air, a frame constituting the furnace and a labyrinth installed at a gate of the furnace, the fumes are cooled to be condensed. Then, when exposed to cooler temperature, the condensed fumes become cohesive solid matter. A lot of solidified fumes, that is, so-called solid fumes adhere to each part constituting the reflow furnace, causing any problems.
For example, when a lot of solid fumes adhere to the conveyor, the circuit board sticks to the conveyor. Thus, at delivery, the circuit board is not separated from the conveyor, and is caught in a sprocket of the conveyor and damaged. When a lot of solid fumes adhere to the fan, rotation of the fan becomes slower, weakening blow-off of hot air. When a lot of solid fumes adhere to the frame, accumulated solid fumes fall off on the circuit board being transferred, soiling the circuit board. When a lot of solid fumes adhere to the labyrinth, the solid fumes contact the circuit boards to cause an electronic component to fall off from a predetermined position.
Thus, in consideration of the problems related to adhesion of these solid fumes, many methods and devices that remove the flux component from the furnace has been proposed in the past. That is, there have been proposed various kinds of soldering devices including a flux recovery device that separates a flux component from a gaseous mixture of the flux component generated in the soldering process and gas derived from the atmosphere in a soldering unit (inert atmosphere, ambient atmosphere), and circulates clean gas in the soldering unit.
Patent Document 1 discloses a flux recovery device that is applicable to a reflow furnace. This flux recovery device includes a centrifuge separator having a cyclone mechanism, which is a dual cylinder consisting of a substantially cylindrical cyclone outer peripheral portion and a substantially cylindrical cyclone inner peripheral portion stored in the cyclone outer peripheral portion. A cooling plate is provided on the outer wall face of the cyclone outer peripheral portion to cool gaseous mixture containing a flux component, which is introduced into the centrifugal separator.
The gaseous mixture flows into the centrifugal separator and forms a spiral downward air flow between the inner wall of the cyclone outer peripheral portion and the outer wall of the cyclone inner peripheral portion, while being cooled with the cooling plate. The flux component, which is cooled and liquidized during this time, is centrifuged and adheres to the inner wall of the cyclone outer peripheral portion. The flux component adhered to the inner wall of the cyclone outer peripheral portion falls along the inner wall of the cyclone outer peripheral portion due to self-weight, and is recovered in a flux storage unit. Thereby, clean air can be delivered to the reflow furnace.
In connection of the flux recovery device, Patent Documents 2 to 5 disclose interior cleaners applicable to a clean room. Each of the interior cleaners includes a water spray device and a detearing cyclone, and the water spray device is connected to a clean room and provides ultrafine water droplets to air discharged from the clean room. The air discharged from the clean room contains dusts. The ultrafine water droplets fill the water spray device. The detearing cyclone is connected to the water spray device, and the air containing water droplets is divided into air and dusts or the like by means of a cyclone flow. This enables clean air to be supplied to the clean room.